The present disclosure relates to video demodulation devices which have a function of demodulating or reproducing a composite video, blanking, and sync signal (a CVBS signal) by digital processing, and which, in particular, are capable of outputting the CVBS signal. More specifically, the present disclosure relates to a technique for preventing lateral blurring of video reproduced from a CVBS signal by achieving stable horizontal synchronization by reducing a noise component included in a horizontal synchronizing signal of the CVBS signal reproduced through demodulation processing in analog telecasting.
Recently, increases in performance and image quality and decreases in costs of video demodulation devices for TV sets have leaded to growing trend toward digitalization of demodulation processing and image processing in analog telecasting.
In demodulation processing of an analog telecasting signal with interference, a low-quality CVBS signal is reproduced, and accordingly, out-of-horizontal-synchronization occurs multiple times in the later video processing, thereby causing lateral blurring of the video. In particular, when an inexpensive tuner is used, a low-quality CVBS signal is likely to be reproduced. Under these circumstances, more importance is placed on digital demodulation devices capable of reproducing a high-quality CVBS signal at reduced costs.
It is known that a noise component included in a horizontal synchronizing signal is a main factor causing the out-of-horizontal-synchronization which results in the lateral blurring of video.
For example, in Japanese Utility Model Publication No. S61-75678, in reproduction of a CVBS signal recorded on a video tape, a pedestal voltage of the input CVBS signal is measured, and a basic voltage of a horizontal synchronizing signal is calculated by subtracting a predetermined value from the measured pedestal voltage. Only during a signaling period of the horizontal synchronizing signal, the basic voltage substituting for the CVBS signal is output, thereby removing a noise component from the horizontal synchronizing signal.
Japanese Unexamined Patent Publication No. 2006-180501 describes a technique related to a video processing device to which a demodulated or reproduced CVBS signal is input. According to this technique, when horizontal synchronization is detected, the input CVBS signal is subjected to noise removal with use of a filter and sliced at a predetermined value, thereby preventing out-of-horizontal-synchronization even when interference occurs.